Polyurethane resin, process for preparing the same and printing ink for laminate containing the same

Abstract

Disclosed is a polyurethane resin which is a reaction product of a high molecular weight polyol compound having a molecular weight of 3,000 to 10,000, a low molecular weight polyol compound having a molecular weight of not more than 200, an organic diisocyanate compound, a chain extender, and optionally a reaction terminating agent, wherein the whole of the high molecular weight polyol compound and the low molecular weight polyol compound has an average molecular weight of 1,500 to 2,700; the isocyanate index (I.I.) of the organic diisocyanate compound to the high molecular weight polyol compound satisfies the following condition: I.I.>2.0; and the nitrogen content of the polyurethane resin derived from the isocyanate group of the organic diisocyanate compound is from 1.30 to 1.95% by weight. The polyurethane resin is useful as a binder for a one-component printing ink for a laminate and exhibits excellent blocking resistance and excellent adaptability for boiling or retorting treatment which meet requirements for a printing ink for a laminate.

What we claimed is: 
     
       1. A printing ink composition for a laminate comprising a polyurethane resin, a coloring agent and an organic solvent as the essential ingredients, the polyurethane resin being a reaction product of a high molecular weight diol compound having a number average molecular weight of 3,000 to 10,000, a low molecular weight diol compound having a molecular weight of not more than 120, an organic diisocyanate compound, a chain extender, and optionally a reaction terminating agent, wherein the whole of the high molecular weight diol compound and the low molecular weight diol compound has a specific average molecular weight (Msp) of 1,500 to 2,700, the specific average molecular weight (Msp) being calculated according to the formula:   Msp=Mw(H)×Mf(H)+Mw(L)×Mf(L)     wherein the abbreviations means the following:   Mw(H): Number average molecular weight of the high molecular weight diol compound,   Mf(H): Mole fraction of the high molecular weight diol compound,   Mw(L): Molecular weight of the low molecular weight diol compound,   Mf(L): Mole fraction of the low molecular weight diol compound, the isocyanate index (I.I.) of the organic diisocyanate compound to the high molecular weight diol compound wherein the isocyanate index (I.I.) means a ratio of the number of equivalents of isocyanate group/the number of equivalents of hydroxyl group, satisfies the following condition: I.I.>2.0; and the nitrogen content of the polyurethane resin derived from the isocyanate group of the organic diisocyanate compound is from 1.30 to 1.95% by weight.   
     
     
       2. The printing ink composition of claim 1, wherein the nitrogen content of the polyurethane resin is from 1.55 to 1.80% by weight. 
     
     
       3. The printing ink composition of claim 1, wherein the number average molecular weight of the polyurethane resin is from 10,000 to 100,000. 
     
     
       4. The printing ink, composition of claim 1, wherein the contents of the polyurethane resin and the coloring agent are from 5 to 20% by weight and from 1 to 50% by weight, respectively. 
     
     
       5. The printing ink composition of claim 1, wherein the low molecular weight diol compound is at least one diol selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, 1,3-cyclohexanediol and 1,4-cyclohexanediol. 
     
     
       6. The printing ink composition of claim 5, wherein the low molecular weight diol compound is used in combination with at least one member selected from the group consisting of glycerin, trimethylolpropane, trimethylolethane, 1,2,3-butanetriol, pentaerythritol and sorbitol. 
     
     
       7. The printing ink composition of claim 1, wherein the organic diisocyanate compound is at least one of an alicylic diisocyanate and an aroaliphatic diisocyanate.